News

Caltrans ordered test for cracks in Bay Bridge steel four years before anchor rods broke

Posted:
04/16/2013 06:53:40 PM PDT

Updated:
04/16/2013 08:32:32 PM PDT

OAKLAND -- At the same time Caltrans was receiving the hefty steel anchor rods that would later snap on the new Bay Bridge, the agency appeared to have growing concerns about the integrity of some high-strength steel components on the span, newly released documents reveal.

In 2008, Caltrans admonished bridge contractor American Bridge Fluor Jt. Venture and subcontractor Dyson Corp. for rushing the test schedule and delivering products that did not meet Caltrans' specifications. Three weeks later, the state ordered an additional surface crack test on a list of other critical steel fasteners.

Caltrans had recorded by that time three instances where steel parts supplied by Ohio-based manufacturer Dyson Corp. and its subcontractors failed to meet specifications, according to the agency's Sept. 16, 2008, nonconformance report, one of hundreds of audit documents released Friday by Caltrans.

The agency had also clashed with American Bridge Fluor, alleging the company ordered the 96 rods that are now the focus of its investigation too late, and Caltrans inspectors had to simultaneously test and release the parts to meet the construction schedule. The state usually tests before it allows shipment.

The broader steel testing directive is among nearly 500 pages released to the media through a Public Records Act request filed after 32 of the 96 high-strength anchor rods on the $6.4 billion replacement eastern span snapped when tightened in March.

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The threaded rod and nut assemblies -- 17 to 24 feet long -- connect the bridge deck and pier columns just east of the main span tower through a shear key, a massive concrete and steel structure that helps control sway during an earthquake.

Caltrans is declining to answer questions about the data and has not said how it will make sure the span is safe in an earthquake or whether it will open on Labor Day as scheduled.

"My expectation is that Caltrans has to be transparent and forthcoming and explain to me and the public what this material means so that we can all understand what has transpired," said DeSaulnier, who will hold a hearing in the next several weeks on the status of the bridge project.

The material that has been released provides no explicit explanation why the 32 rods may have snapped, but it makes clear the agency's ongoing concerns about the suppliers involved.

Among other details in the documents:

In advance site visits in 2007 and 2008, Caltrans auditors conditionally approved as a steel component manufacturer Dyson Corp. of Painesville, Ohio; heat treater TC Industries of Crystal Lake, Ill.; dry grit blaster Phoenix Industries and galvanizer Monnig Industries, both of Glasgow, Mo. Inspectors identified concerns they said must be resolved before the work could be done, such as improved product traceability and adequate documentation.

TC Industries subsequently lost the paperwork associated with the heat treatment of 96 anchor rods in 2008 -- the same batch where 32 later broke -- and had to put the steel through the process a second time.

Metallurgists say reheating could make the rods too hard or too soft. But the bolts passed all of Caltrans' material properties tests except for a slight variation on one of the measurements, and the state later accepted them.

While many Bay Area residents are just learning what plagues high-strength steel on the Bay Bridge, Caltrans has clearly been thinking about it for years.

For reasons the agency has not explained, Caltrans in October 2008 directed American Bridge Fluor to conduct special magnetic particle testing on eight types of steel fasteners that will be under loads of 50 percent or more.

The list includes the east saddle tie rod and the anchor rods for the main cable, cable bracket, bearings and shear keys.

The liquid is wiped away and the magnetic levels are analyzed under the premise that fluid would have seeped into any existing cracks. Surface cracks allow water to seep into the steel, which can lead to corrosion and leave the fastener vulnerable to a phenomenon called hydrogen embrittlement. When that happens, the bolt becomes fragile and can snap when under load.

Caltrans has pointed to hydrogen assault -- either during production or while they were exposed to the elements -- as the likely culprit in the fasteners that broke in March.

The fractured rods, among the 96 fasteners manufactured in 2008, were not subjected to magnetic particle testing for reasons that Caltrans hasn't disclosed.

The test was performed on 192 bolts fabricated in 2010 for adjacent shear keys and bearings. Those bolts have not failed.

But even if the first batch of rods had been subjected to the particle test, it may not have predicted that a shocking third of the bolts would fail 4½ years later, said Robert Ritchie, a senior scientist at Lawrence Berkeley Laboratory and a UC Berkeley professor of mechanical engineering.

While the test would show the presence of surface cracks, it would not reveal internal fracturing or foretell a failure in the protective zinc coating, he said.

A fracture mechanics test is a better way to detect weak steel, Ritchie said.

It involves notching a steel sample and measuring the amount of force it takes to break the steel while it is under load or stress. The test is mandated in the nuclear industry but rarely used for road construction, he said.

But failures such as these are rarely the result of a single missed test or a simple manufacturing glitch, he added.

"These things are usually a series of things that come together," Ritchie said. "Any one of the factors on its own might not be a problem, but when you combine them, you end up with a disaster."

Caltrans officials say they don't know how 32 high-strength threaded steel anchor rods in the new Bay Bridge weakened and snapped. State engineers suspect hydrogen embrittlement, a well-known phenomenon where the element infiltrates the spaces between the steel's crystalline grains and loosens its bonds. But is that really what happened? Metallurgical and materials sciences experts weigh in:

Q: Could sitting in water really lead to brittle steel?A: Yes, water could corrode the protective zinc coating and leave steel vulnerable to hydrogen invasion when contractors tightened the nuts and put stress on the rods, UC Berkeley metallurgical engineer and professor Tom Devine said.

But given that an extraordinary third of the 96 bolts broke, it is more likely that a flaw in the steel made the rods exceptionally susceptible to fracturing, Devine said.

Q: Were the nuts over-tightened?A: It's possible, said Robert Ritchie, a senior scientist at Lawrence Berkeley Laboratory and a UC Berkeley mechanical engineering professor.

"If engineers did the calculation wrong or applied too much torque, this would definitely result in a higher stress in the bolt, and with such a high-strength steel, this is a prime recipe for trouble," he said.

Q: If engineers were worried about corrosion, why didn't they use stainless steel?A: Stainless steel is more resistant to corrosion and hydrogen embrittlement, but it usually lacks sufficient strength required, and it is much more expensive, Ritchie said.